The present invention relates to a method of manufacturing a rotor assembly for an electric motor and an improved rotor assembly which includes a novel molded rotor core and a novel manner of molding and assembling such rotor core with a rotor shaft extending therethrough, including a unique arrangement for an oil return tube.
As is set forth in both prior coassigned U.S. Pat. Nos. 4,209,722, and 4,499,661, both issued to C. Theodore Peachee, Jr., on June 24, 1980, and Feb. 15, 1985, respectively, in certain dynamoelectric machines of the induction motor type, and particularly in many smaller motors sometimes referred to as unit bearing motors, the motors have a squirrel cage rotor assembly in which the conductor bars for the rotor and the end rings of the rotor are made of die cast aluminum. Typically, these rotor assemblies include a stack or rotor core of individual laminations constructed from suitable ferro-magnetic material. Each lamination has a central opening and a plurality of satellite openings or slots adjacent its outer margin. The laminations are assembled in a stack and the laminations are rotated slightly with respect to one another in the stack so that their central openings are coaxial but so that their slots are skewed relative to one another and so that the slots constitute passages. The lamination stack or core is then placed in a suitable die casting mold and molten aluminum is injected under pressure into the mold to fill the mold, to flow through the skewed passages in the core formed by the slots so as to form the conductor bars of the rotor and to form the rotor end rings. These die cast squirrel cage rotors typically have a central opening therethrough and a rotor shaft extending through this opening which is rigidly secured to the rotor so that the shaft rotates with the rotor. This central opening may be defined at least in part by the central opening of the laminations and is appreciably larger than the shaft so as to receive a rigid boss of the motor housing. The rotor shaft is received in an opening in the boss and is journalled therein by a suitable journal bearing or the like so as to rotatably support the rotor on the motor housing. As is typical, a portion of the rotor shaft journalled in the bearing has a helical oil groove formed on its outer surface and the outer end of the shaft rotates in a felt wick supplied with lubricating oil from a reservoir. Upon rotation of the rotor, the oil grooves in the shaft pick up oil from the wick and move it along the length of the bearing to lubricate it. Upon the oil being discharged from the inner end of the bearing, it is slung outwardly by the centrifugal force of the rotating rotor shaft.
In prior art motors having such rotors, a return system was provided for recirculating the oil to the oil supply reservoir. This oil return system typically included a tubular oil return member which was fitted into the opening in the rotor after die casting. This oil return member surrounded the bearing boss and extended out beyond the end of the rotor. The inner end of this oil return member was sealed to the rotor body by application of a sealant. An outer end cap carried by the motor housing surrounded the outer end of the oil return member and collected oil which flowed out of the end of the oil return member from the inside of the rotor.
In the manufacture of these prior art die cast squirrel cage rotors, it has heretofore been difficult to fit the oil return member into the rotor body and to seal the inner end of the oil return member to the rotor body. As mentioned above, the sealing operation usually involved the application of a sealant to the joint between the inner end of the oil return member and the rotor body. However, many of the motors which incorporated these die cast squirrel cage rotors were relatively small and the space in which the sealant had to be applied was cramped. Also, the application of sealant was a messy and time-consuming operation performed after die casting of the rotor thus resulting in increased labor costs for the manufacture of the motor.
In prior coassigned U.S. Pat. No. 4,209,722, a die cast rotor is disclosed in which a tubular oil return member is sealably die cast-in-place within the rotor body. However, this die cast-in-place oil return member was separate and apart from a securement member which was also die cast-in-place within the rotor body, this securement member receiving and rigidly securing the rotor shaft to the rotor body. Typically, this rotor shaft securement member was made of brass. During die casting of the rotor, it was necessary to separately locate or place both the oil return tube and the rotor shaft securement member in the die cavity of the die casting machine. The placement of these two parts required a certain degree of skill and time on the part of the operator of the die casting machine.
In prior coassigned later U.S. Pat. No. 4,499,661, the oil return tube and rotor shaft mounting member are integrally formed as one piece by cold extrusion and inserted within the central opening of a rotor core including a lamination stack. Molten metal is then die cast around the one piece oil return and rotor shaft mounting member and around the core, and the rotor shaft is then fixedly secured to the rotor shaft mounting member of the extruded integral piece. This later U.S. Pat. No. 4,499,661 enhanced rotor assembly over the previous teachings in the art, eliminating assembly parts with the oil return tube serving as a locater for the rotor core in assembly operations, providing an economical way to manufacture the rotor assembly with reduced scrap and with reliable operation.
The present invention provides a new and useful method of manufacture and a unique structural rotor assembly which can be produced by an even more straightforward and efficient series of manufacturing steps, and which provides a rotor assembly of even greater reliability in operation, further extending the life of the motor in which it is employed. In this regard, the present invention provides a novel method and rotor assembly arrangement which provides for an optimization of resistance control in the rotor assembly with a minimum of molten materials through a comparatively simple, straightforward series of manufacturing steps, including a unique, straightforward assembly step with respect to the oil return tube and which, at the same time, provides for efficient oil distribution operations with a tight seal between the several parts of the assembly. In addition, the unique method and apparatus of the present invention, recognizing the undesirability of oil losses, minimizes the porosity of those parts which are contacted with oil and, at the same time, ensures effective recycling of such oil with a minimum of sealing parts. Further, the present invention permits for a reduction in costly secondary machining operation and also allows for the selective scrapping of parts which might appear to be defective during manufacturing quality inspection procedures.
Various other advantageous features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.